(a) Field of the Invention
This invention relates to a base plate to be used as a recording disc, on which a recording medium is to be maintained. More particularly, it is concerned with a method for manufacturing a glass base plate for disc to hold thereon a high density recording medium such as magnetic recording medium, etc., and also to such base plate for the recording disc.
(b) Description of Prior Arts
In the field of magnetic recording, a hard magnetic disc having high recording density comprises a base plate with a flat and smooth surface, and a recording medium of highly saturated magnetic density, for example, a magnetic metal thin film such as Co-Cr, Co-Ni, etc., placed on the base plate. This type of recording disc has its own problem such that, since its surface is extremely flat and smooth, there takes place adsorption between the magnetic head and the recording medium due to intervention of moisture in the air to result in crush of the magnetic head. With a view to solving this problem of head crush or "micro-tribology", there have so far been adopted various methods for lowering the frictional coefficient of the disc surface, such as slightly oxidizing the surface of a magnetic thin film of, for example, Co-Cr; or placing a solid lubricating material (e.g., carbon film) or a liquid lubricant on the surface on the base plate; or increasing surface coarseness of the base plate by subjecting it to a texturing treatment (a treatment to increase the surface coarseness of the base plate) through tape lapping or polishing. Such treatments are generally called "mechanical texturing".
The above mentioned mechanical texturing, however, has its disadvantage such that, due to occurrence of burns, etc., or irregular surface conditions, etc., there is a large partial differene in the surface coarseness (Ra) of the base plate with the consequence that it is easily scratched during sliding of a magnetic head on it. On account of such large difference in the surface coarseness, it is not possible to bring the magnetic head sufficiently close to the magnetic recording medium, which not only makes it difficult to realize the low bouyancy of the magnetic head required for effecting the high density recording, but also poses a problem on its CCS-resistant property. As an expedient for solving such problems, it has been admitted that the chemical texturing treatment, as disclosed in Japanese Patent Application No. 62-243074 is useful. The base plate for the disc, which has been subjected to this treatment is very small in variations of frictional coefficient due to continuous sliding of the magnetic head.
The present invention proposes an improved texturing technique, by which the surface of crystallized glass used as the base plate for the disc is subjected to an etching treatment to form uniform and regular convexities and concavities on the surface of the glass base plate.